1. Field of the Invention
The invention relates to elongated, powered surgical instruments for use in endoscopic tissue resection. More particularly, the invention relates to an instrument having an elongated inner tube rotatably situated within an elongated stationary outer tube, both inner and outer tubes having, at their distal ends, cutting apertures which cooperate to resect or otherwise affect tissue during endoscopic surgical procedures. Still more particularly, the invention relates to an instrument and the method of manufacturing an instrument in which the cutting apertures at the distal ends of the elongated tubular members of a rotatable surgical instrument are shaped to enhance end-cutting.
2. Description of the Prior Art
The use of elongated surgical cutting instruments has become well accepted in performing closed surgery such as arthroscopic or, more generally, endoscopic surgery. In closed surgery, access to the surgical site is gained via one or more portals, and instruments used in the surgical procedure must be elongated to permit the distal ends of the instruments to reach the surgical site. Surgical cutting instruments for use in closed surgery--also known as "shavers"--conventionally have a straight, elongated outer tubular member terminating at a distal end having an opening in the end or side wall (or both) to form a cutting port or window and a straight, elongated inner tubular member concentrically disposed in the outer tubular member and having a distal end disposed adjacent the opening in the distal end of the outer tubular member. The distal end of the inner tubular member has a surface or edge for engaging tissue via the opening in the outer tubular member and in many cases (but not all) cooperates with the opening to shear, cut or trim tissue. In some cases, such as burrs, the opening in the outer tube merely allows access to the tissue and does not otherwise cooperate to resect tissue. The inner tubular member is rotatably driven about its axis from its proximal end, normally via a handpiece having a small electric motor which is controlled by finger actuated switches on the handpiece, a foot switch or switches on a console supplying power to the handpiece. The distal end of the inner tubular member can have various configurations depending upon the surgical procedure to be performed, and the opening in the distal end of the outer tubular member has a configuration to cooperate with the particular configuration of the distal end of the inner tubular member. For example, the inner and outer tubular members can be configured to produce whisker cutting, synovial resection, arthroplasty burring or abrading, side cutting, meniscus cutting, trimming, full radius resection, end cutting and the like, and the various configurations are referred to generically as shaver blades. Cut tissue is aspirated through the hollow lumen of the inner tubular member to be collected via a vacuum tube communicating with the handpiece.
The aforementioned elongated surgical cutting instruments have also been produced in angled configurations in which the distal tips of the inner and outer members are aligned and offset or bent at either a fixed or variable angle from the proximal ends of the aligned inner and outer members. Examples of fixed and variable angle rotary surgical instruments are shown in U.S. Pat. Nos. 4,646,738 (Trott) and 5,411,514 (Fucci et al.), both assigned to the assignee hereof, and incorporated by reference herein. In other respects the operation of fixed and variable angle shavers is largely the same as that of the straight shavers described above.
One parameter affecting the efficiency of operation of shaver blades is sharpness of the edges of the windows. Various prior art designs are known to have differing degrees of sharpness of both the inner cutting edges and the periphery of the outer window. Additionally, end-cutting applications require that the blades be capable of cutting tissue presented axially or substantially axially. The present invention is concerned with the design and manufacture of an outer tubular member having not only a sharpened window periphery in a lateral direction, but also a sharpened end-facing structure.
General purpose shaver blades (sometimes known as microdebriders) have outer tubes formed by rolling over the end of the tube so that it forms a hemispherical radius. The inner tube is similarly shaped. When cutting edges are formed on the inner and outer tubes the geometry produced is most efficient for resection of tissue presented laterally. Because of the hemispherical distal end shape, the cutting edges are not as efficient in engaging tissue when it is presented axially or at shallow angles to the tube axis.
Special purpose end-cutting shaver blades have been produced in an attempt to overcome this limitation. These differ from the aforementioned blades in that the distal end of the outer tube is not hemispherical but rather is formed with a much smaller radius so as to produce a relatively flat distal surface perpendicular to the axes of the elongated inner and outer tubular members. The cutting window at the distal end of the outer member has both end-facing and lateral-facing portions and the cutting window at the distal end of the inner member has a periphery adapted to grab tissue presented end-wise between the end-facing cooperating teeth or edges of the inner and outer members. While effective for certain tissue, prior art designs have proven ineffective for other tissue such as, for example, ethmoid bone encountered in various ENT (ear-nose-throat) procedures. Prior art end cutters are known which have the diameter of this flat distal surface equal to approximately 70% of the diameter of the body of the outer tube. The flat, end-facing surface is not equal to the tube diameter because the circumferential junction at the transition between the flat distal surface and the cylindrical wall of the outer tubular member has a radius. This radius and the flat nature of the distal surface limit the ability of prior art end-cutting shaver blades to get close (axially) to relatively flat tissue surfaces (such as bone or other firm tissue). The effectiveness of these cutters is also compromised for shallow angle resection. Additionally, the cutting edge geometries of these blades are such that only the distal tip area has low included angle cutting edges. This makes the blades inefficient for side cutting and susceptible to clogging due to tissue wrap.
It is known that improved resection efficiency is achieved by sharpening the cutting edges and this is true of conventional scissors as well as endoscopic shavers although the manufacture of the latter is considerably more difficult. The smaller the included angle of the cutting edge, the sharper the edge. Clearly, below a certain limit the edge becomes too delicate to be practical. When applied to the tubular members of cylindrical, rotating shavers, the cutting window on the inner member and the cutting window on the outer member each have peripheries which are the cooperating edges which rotate cyclically past each other and which should have the smallest included angles in order to produce sharp edges for most efficient resection. U.S. Pat. No. 5,693,063 (VanWyk et al.), assigned to the assignee hereof and incorporated by reference herein, discloses new shaver blade designs and technology which can be incorporated into the invention claimed herein to overcome the disadvantages of prior art end cutters. This technology not only enables production of sharper edges, but also enables the edges to be placed closer to target tissue by minimizing the thickness of the window perimeter.
It is accordingly an object of this invention to produce a shaver blade assembly in which the windows of the inner and outer members have a sharpened periphery.
It is also an object of this invention to produce an end-cutting shaver blade assembly having an outer member with a sharpened, end-facing window formed by a peripheral land surface angled to the window rim.
It is another object of this invention to produce a sharpened outer window of an end-cutting shaver blade with a simple process minimizing the use of complex tools and the number of required processing steps.
It is yet another object of this invention to produce an end-cutting shaver blade capable of getting closer to tissue presented end-wise than prior art end-cutting shavers.